1. Field of the Invention
The present invention is generally directed to a toner containing binder resin and colorant in which the binder resin is a polyester having both low molecular weight, high melt flow index value linear portions and crosslinked portions, as well as developer containing such toner. More specifically, the present invention relates to a toner having a high loading amount of colorant and a polyester resin binder that contains both linear and crosslinked portions, but which has a satisfactorily high melt flow index to enable longer fuser roll life while simultaneously minimizing the presence of objectionable gloss non-uniformity defects in the prints produced by a xerographic engine.
2. Discussion of Related Art
Toners comprised of binder resins that include a linear portion as well as a portion of crosslinked microgel particles are kown. U.S. Pat. Nos. 5,227,460, 5,352,556, 5,376,494, 5,395,723 and 5,401,602, each incorporated herein by reference in its entirety, describe a low melt toner resin with low minimum fix temperature and wide fusing latitude that contains a linear portion and a crosslinked portion containing high density crosslinked microgel particles, but substantially no low density crosslinked polymer. It is described that the resin may be formed by reactive melt mixing under high shear and high temperature of an unsaturated polyester resin such as a poly(propoxylated bisphenol A fumarate) in the presence of a chemical initiator that hag been mixed into the polyester.
U.S. Pat. No. 6,063,827, incorporated herein by reference in its entirety, describes a process for the preparation of an unsaturated polyester which comprises (i) reacting an organic diol with a cyclic alkylene carbonate in the presence of a first catalyst to thereby form a polyalkoxy diol, (ii) optionally adding thereto a further amount of cyclic alkylene carbonate in the presence of a second catalyst, and (iii) subsequently polycondensing the resulting mixture with a dicarboxylic acid. The unsaturated polyester formed may then be further subjected to crosslinking with an initiator as in the patents described immediately above in order to form a toner resin.
Co-pending U.S. application Ser. No. 09/520,439, filed Mar. 7, 2000 allowed an incorporated by reference herein in its entirety, describes toners and developers for particular use in devices utilizing hybrid scavengeless development, the toners including toner particles of at least one binder, at least one colorant, and optionally one or more additives, the toner exhibiting a charge per particle diameter (Q/D) of from xe2x88x920.1 to xe2x88x921.0 fC/xcexcm with a variation during development of from 0 to 0.25 fC/xcexcm and the distribution is substantially unimodal and possesses a peak width of less than 0.5 fC/xcexcm, and the toner has a triboelectric charge of from xe2x88x9225 to xe2x88x9270 xcexcC/g with a variation during development of from 0 to 15 xcexcC/g following triboelectric contact with carrier particles. A desired range of rheology or melt flow index (MFI) for a toner is also described. The developer of a mixture of carrier particles and the toner particles has a triboelectric value of from xe2x88x9235 to xe2x88x9260 xcexcC/g, a charge distribution (Q/D) of from xe2x88x920.5 to xe2x88x921.0 fC/xcexcm and the distribution is substantially unimodal and possesses a peak width of less than 0.5 fC/xcexcm, preferably less than 0.3 fC/xcexcm, and a conductivity of the developer ranges from 1xc3x9710xe2x88x9211 to 10xc3x9710xe2x88x9215 mho/cm as measured at 30 V. The method of forming the toner having controlled properties includes feeding at least one binder and at least one colorant into a mixing device at a feed ratio, then upon exit of the mixture from the mixing device, monitoring one or more properties of the mixture with at least one monitoring device, wherein if the monitoring indicates that the one or more properties being monitored is out of specification, removing the monitored mixture from the method and adjusting the feed ratio by adjusting the feeding of the at least one binder or of the at least one colorant, thereby retaining in-specification mixture in the method, grinding the in-specification mixture, optionally together with a portion of one or more external additives to be added to the mixture, classifying the ground in-specifcation mixture, and mixing the classified in-specification mixture with one or more external additives to obtain the toner having controlled properties.
Co-pending U.S. application Ser. No. 09/695,861, filed Oct. 26, 2000 allowed and incorporated by reference herein in its entirety, describes a toner resin having linear portions and crosslinked portions of high density microgel particles, where the linear portions of the toner resin are an unsaturated polyester resin, preferably poly(propoxylated bisphenol A fumarate). The toner resin is prepared so that the crosslinked resin achieved contains less than 0.20 percent by weight of acids. In particular, the crosslinked toner resin is free of benzoic acid. The method of making the toner resin includes (a) spraying a liquid chemical initiator such as 1,1-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane onto the unsaturated polyester resin prior to, during or subsequent to melting of the unsaturated polyester resin to form a polymer melt; and (b) subsequently crosslinking the polymer melt under high shear to form the crosslinked toner resin. The resin is reported to most preferably have a rheology such that the MFI is about 18 to about 20 g/10 min at 125xc2x0 C. and 16.6 kg load, preferably about 19.5 g/10 min.
Co-pending U.S. application Ser. No. 09/671,997, filed Sep. 29, 2000 and incorporated by reference herein in its entirety, describes at least three differently colored toners, designed for use together in forming a color image in an image developing device, that have substantially the same melt flow index value. By substantially matching the melt flow index values of at least three toners of a set of toners, it has been found that the resultant color image has an overall excellent image quality, i.e., an excellent overall gloss level without any gloss banding. The toners may be made to have substantially the same melt flow index value in a carefully controlled process that includes forming a single toner by feeding at least one binder and at least one colorant into a mixing device to form a mixture, upon exit of the mixture from the mixing device, measuring a rheology property of the mixture with at least one monitoring device, and comparing the measured rheology property to a target property range that the measured rheology property must be within in order for the single toner to achieve the desired melt flow index value, wherein if the measuring indicates that the rheology property is outside of the target property range, feed amounts of the at least one binder or of the at least one colorant into the mixing device are adjusted, grinding the mixture, optionally together with a portion of one or more external additives to be added to the mixture, classifying the ground mixture, mixing the classified mixture with one or more external surface additives to obtain the single toner having the desired melt flow index value, and repeating the steps for each additional differently colored toner.
As discussed in this co-pending application, by carefully controlling the melt flow index values to be substantially the same for as many of the different color toners that develop a color image in the same device as possible, the resultant color image has an overall excellent image quality. In particular, the color image has an excellent overall gloss level and does not exhibit any differential gloss (distinctly different glosses among different colors) or gloss banding (variations in gloss from one area of an image to another within a single color). The melt flow index (MFI) is a value identifying the rheology, or viscoelasticity, of the toner. MFI as used herein is defined as the weight of a toner (in grains) which passes through an orifice of length L and diameter D in a 10 minute period with a specified applied load, unless otherwise indicated.
However, some toners require the presence of high amounts of colorant (e.g., pigment) in order for the toner to exhibit satisfactory gloss. For example, as noted in this co-pending application, yellow toner requires a higher amount of colorant than the other traditional colors (cyan, magenta and black) of a four color toner set. The amount of colorant inversely impacts the MFI of the toner, i.e., the more colorant that is present in the toner, the lower is the MFI of the toner. For toners having higher loading amounts of colorant, it is thus difficult to achieve a final toner having a satisfactorily high MFI.
What is still desired is a toner composition that contains higher amounts of colorant and still also exhibits a satisfactorily high MFI.
It is thus an object of the present invention to develop a toner composition that possesses a satisfactorily high melt flow index at higher colorant loadings.
It is a still further object of the present invention to develop a toner composition that exhibits high gloss and also lengthens a fuser roll life.
It is a still further object of the present invention to develop a toner composition that is able to match melt flow index and gloss properties of other toner compositions to be used together in a developer set of toners, despite different colorant loading amounts among the different toner compositions within the developer set.
These and other objects are achieved by the present invention, wherein in embodiments the invention relates to a toner comprising a binder and at least one colorant, wherein the binder comprises a polyester resin having linear portions and crosslinked portions of high density crosslinked microgel particles, wherein the linear portions have a melt flow index value of at least about 40 MFI units, wherein the binder contains at least about 5% by weight of the crosslinked portions, wherein the at least one colorant comprises at least about 6% by weight of the toner exclusive of any surface additives, and wherein the toner has a melt flow index value of about 11xc2x13 MFI units.
In further embodiments, the invention relates to a toner comprising a binder component and at least one colorant, wherein the at least one colorant comprises at least about 6% by weight of the toner exclusive of any surface additives, wherein the binder component comprises about 10% to about 70% by weight of a first polyester resin having a melt flow index value of from about 25 to about 35 MFI units and about 30% to about 90% by weight of a second polyester resin having a melt flow index value of at least about 40 MFI units, and wherein the toner has a melt flow index value of about 11xc2x13 MFI units.
In still further embodiments, the invention relates to a developer set comprising at least four differently colored toners for use together in a same image developing device, wherein each of the at least four differently colored toners comprises a binder component and at least one colorant, wherein each of the at least four differently colored toners has a melt flow index value of about 11xc2x13 MFI units, and wherein at least one of the differently colored toners comprises a toner according to the present invention.